Cylinder drifts

A) Piston seal(s) leak


B) Directional control valve leaks


C) Sufficiently high return line back pressure (single acting cylinder)

A) Disassemble and replace seals.

B) Refer to section on directional control valve maintenance.

C) Check for restricted return line; remove and replace return line filter.

Cylinder does not move the load when the directional valve is actuated

A) Binding of linkage arrangement

B) Piston rod bent or broken



C) Piston seal(s) leak

A) Check linkage for proper alignment

B) Disassemble and replace rod. Check for proper mounting alignment.

C) Disassemble and replace seals.

Leakage between body and end caps

A) Hard and/or brittle seals




B) Pressure too high





C) Crushed or extruded seal

A) Check for excessive operating temperature. Remove and replace with heat tolerant seals.

B) Pressure should be lower, adjust to rated limit. Measure pressure inside cylinder during cushioning. Use external shock absorbing device.

C) Check seal and fluid compatibility. Replace with seals that are compatible with fluid. Re torque tie rods properly; check manufacturer specifications.

Internal seal leakage

A) Extreme back pressure





B) Soft or mushy seals



C) Hard and/or brittle seals

A) Check flow control adjustment and correct if necessary. Check internal cushion adjustment and correct of necessary.

B) Check compatibility of seals and fluid. Replace with compatible seals.

C) Check for excessive operating temperature. Remove and replace with heat tolerant seals.

Rod gland seal leaks

A) Nicked, worn and/or scored rod and seals



B) Loose retainer or bushing



C) Hard and brittle seals

A) Check rod for damage; replace. Check for normal seal wear with .002 feeler between seals and rod. Should be tight.

B) Adjust retainer until leakage stops (v-packing). Remove and replace v-packing.

C) Check for excessive operating temperature. Remove and replace with heat tolerant seals.

Cylinder operates erratically

A) Cylinder leaks internally








B) Aeration of system






C) Directional valve not shifting

A) Repair and/or replace parts and seals. Check fluid viscosity using a visgauge or through oil analysis. Compare to equipment manufacturer's specification. Check for contamination; flush, clean and refill system.

B) Bleed the system of air. Check pump intake with vacuum gauge. Fix any leaks. Check for low fluid level. Check for fluid return line in tank above fluid level. Extend return line.

C) Disassemble and clean; reassemble. Check pilot pressure, too low. Check for system aeration. Check for contamination and wear.